1. Field of the Invention
The invention pertains to a damping valve assembly for a vibration damper having a piston which moves in a damping medium in a cylinder, the assembly including a first damping valve which, in a first operating range, opens as the flow velocity of the damping medium increases; and a first control slide which, in a second operating range with a progressive damping characteristic, can move in a closing direction to close a throttle.
2. Description of the Related Art
DE 35 33 386 A1 describes a two-tube vibration damper, the piston of which carries a compression spring. The spring moves a control slide on a bottom valve into a closed position as a function of the stroke of the piston to produce a progressive damping force characteristic shortly before the end of the stroke. In a vehicle being driven at comparatively high speed over a section of bad road, it is possible for a wheel to move inward very abruptly and to be braked along the further course of its inward travel by the maximum damping force available, which is determined by a set of valve disks on the bottom valve. If the stop spring then meets the control slide on the bottom valve side of the damper, only a comparatively small amount of residual stroke is left to absorb the energy of the inward-traveling wheel. It is possible for the area of the vehicle body connected to the vibration damper to be affected by this unabsorbed force.
What appears to be the simplest possibility at first glance is simply to reinforce the vehicle body in the endangered area, but this would make it necessary to accept a considerable increase in weight.
Another disadvantage of this principle is that the stop spring on the piston side causes a real loss of stroke. In this context, DE 36 02 224 A2 should also be mentioned, which describes the same operative principle.
GB 2,070,730 discloses a vibration damper, which has a damping valve device with two valves, which are connected hydraulically in parallel. A first damping valve comprises a throttle cross section, which, as the speed of the piston rod increases, is reduced in size by a valve body, e.g., an elastic disk, as a function of the speed of the piston rod, so that a progressive damping force characteristic is obtained. If the load becomes excessive, a pressure-relief valve, which connects the two working spaces of the vibration damper to each other, can go into effect. Various problems occur in practice when the solution according to DE 31 07 517 A1 is used. For example, the damping force is very small at comparatively low speeds and then increases parabolically, so that, as the vehicle is being driven, a more-or-less spongy and imprecise feeling is conveyed. Even at low speeds, it is desirable to perceive a certain measure of damping force. When the piston rod travels at an intermediate speed, the damping force should follow a degressive or linear characteristic and should not show a progressive damping force behavior until very high piston speeds. A damping force characteristic of this type can be achieved with a small pilot cross section, which in many cases remains open at all times, to which a spring-preloaded damping valve is connected hydraulically in parallel, which opens only after the speed of the piston exceeds a certain defined value.